Actually, the phenomenon hasn't gone anywhere and there's been gobs of mainstream coverage of its continued existence right into the modern internet age. One good example:
Unidentified radio broadcasts have been transmitting coded messages, using numbers for years
www.radioworld.com
There are also articles discussing their continued use into the past decade or so from
Vice,
Popular Mechanics,
Gizmodo, the
BBC,
NPR, and
Wired.
Their financial straits are dire in deed, but dictatorships have never been known to spare any expense on their intelligence activities, no matter how many of their peoples are living without access to food, basic services, or electricity. Staying in and securing their power is the primary goal, alas.
I've seen people speculating for decades that some countries run them as decoys, like to convince foreign nations that their spies were deployed throughout the world. But that logic has never made sense. Every intelligence agency knows all the other countries' intelligence agnecies spy, on friends or foes alike. There would be no point in running huge shortwave transmitters broadcasting garbage messages just to imply something everyone either already knows, or would never be negligent enough not to just assume.
As far as proof they're used by spies, that's not a matter of speculation anymore. For many decades there wasn't any, but court convictions with publicly presented proof began happening in the late 20th century and continued into the last couple decades. You can find a bunch of examples at
https://en.wikipedia.org/wiki/Numbers_stations#History, including more than a couple cases of spies in America being caught using Cuba's numbers station in particular. (The Radio World article above also mentions one of the Cuban numbers station cases involving spies working in the U.S.)
I know people are down on Wikipedia around here, but seriously, just read that section. The citations are good, and when the Internet Archive finishes fixing all the damage done by the cyberturds who hacked it recently, they'll actually be readable.
Also, great citations
@boombox4!